Search

The DEAP-3600 experiment is located 2 km underground at SNOLAB, in Sudbury, Ontario. It is a single-phase detector that searches for dark matter particle interactions within a 1000-kg fiducial mass target of liquid argon. A first generation prototype detector (DEAP-1) with a 7-kg liquid argon target mass demonstrated a high level of pulse-shape discrimination (PSD) for reducing β/γbackgrounds and helped to develop low radioactivity techniques to mitigate surface-related αbackgrounds. Construction of the DEAP-3600 detector is nearly complete and commissioning is starting in 2014. The target sensitivity to spin-independent scattering of Weakly Interacting Massive Particles (WIMPs) on nucleons of 10−46cm2will allow one order of magnitude improvement in sensitivity over current searches at 100 GeV WIMP mass. This paper presents an overview and status of the DEAP-3600 project and discusses plans for a future multi-tonne experiment, DEAP-50T.

The TRIUMF-ISAC gamma-ray escape-suppressed spectrometer (TIGRESS) is a new γ-ray detector array being developed for use at TRIUMF's Isotope Separator and Accelerator (ISAC) radioactive ion beam facility. TIGRESS will comprise 12 32-fold segmented clover-type HPGe detectors coupled with 20-fold segmented modular Compton suppression shields and custom digital signal processing electronics. This paper provides an overview of the TIGRESS project and progress in its development to date.

The structure function ratiosF

We have studied transverse momentum distributions for exclusiveρ0 muoproduction on protons and heavier nuclei at 22<25 GeV2. TheQ2 dependence of the slopes of thept2 andt′ distributions is discussed. The influence of the non-exclusive background is investigated. Thept2-slope for exclusive events is 4.3±0.6±0.7 GeV−2 at largeQ2. Thept2 spectra are much softer than inclusivept2 spectra of leading hadrons produced in deep inelastic scattering.

We have used the eukaryotic DNA polymerase α inhibitor, aphidicolin, and the polymerase β inhibitor, dideoxythymidine, to examine the role of these enzymes in excision repair of ultraviolet (u.v., 254 nm) damage induced in non-dividing (arrested) human skin fibroblasts. The effects of these drugs on u.v.-treated cells have been monitored using a simple and reproducible repair synthesis assay in parallel with viability measurements to determine the degree of inhibition of repair of potentially lethal damage. In agreement with previous studies using density gradients, repair synthesis induced by low fluences of u.v. (< 3 J m-2) is relatively insensitive to inhibition by aphidicolin compared to high fluences where approximately 85 per cent inhibition is observed at the highest (20 μg/ml) aphidicolin concentration employed. However, repair of potentially lethal damage is inhibited by at least 90 per cent over the entire fluence range. Although dideoxythymidine led to considerable inhibition of repair synthesis, the result is probably an artifact under these in vivo conditions. The polymerase β inhibitor was not toxic to u.v.-treated cells nor did it add to the toxicity of aphidicolin when the drugs were used in combination. We conclude that if the β polymerase is involved in excision repair then its temporary (4 h) inhibition by dideoxythymidine is entirely reversible. In contrast, polymerase α appears to be an enzyme essential to the majority of biologically effective excision repair over the entire u.v. fluence range tested.

Summary PAPP-A is a macromolecular glycoprotein associated with human pregnancy. In vitro, PAPP-A is produced by explant cultures of trophoblast and decidua. The present work was undertaken to see if the presence of decidua had any effect on the disappearance rate of PAPP-A after removal of the placenta either by surgery or by spontaneous delivery. PAPP-A was measured before and at different times after a normal delivery (n = 6), after a termination of early pregnancy (n = 11) and after surgery for ectopic pregnancy (n = 8).

Mutations induced by UVB (313-nm) radiation, a wavelength in the region of peak effectiveness for sunlight-induced skin cancer in humans, have been analyzed at the sequence level in simian cells by using a plasmid shuttle vector (pZ189). We find that significant differences exist between the types of mutations induced by this solar wavelength and those induced by nonsolar UVC (254-nm) radiation. Compared with 254-nm radiation, 313-nm radiation induces more deletions and insertions in the region sequenced. In addition, although the types of base substitutions induced by the two wavelengths are broadly similar (in both cases, the majority of changes occur at G-C base pairs and the G-C to A-T transition is predominant), an analysis of the distribution of these base changes within the supF gene following irradiation at 313 nm reveals additional hot spots for mutation not seen after irradiation at 254 nm. These hot spots are shown to arise predominantly at sites of mutations involving multiple base changes, a class of mutations which arises more frequently at the longer solar wavelength. Lastly, we observed that most of the sites at which mutational hot spots arise after both UVC and UVB irradiation of the shuttle vector are also sites at which mutations arise spontaneously. Thus, a common mechanism may be involved in determining the site specificity of mutations, in which the DNA structure may be a more important determinant than the positions of DNA photoproducts.

Abstract.: A search for the production of a bound trineutron state has been performed using the reaction 3He(π−,π+)nnn at incident pion energies of 65, 75, and 120 MeV. No evidence for the existence of the 3n was found, and an upper limit for the production cross section of approximately 30 nb/sr (2σ confidence level) was obtained.